1. Field of the Invention
This invention relates to a ceramics material (or member) and a method of producing it, and more particularly to a ceramics material that shows an excellent plasma-resistant property in an atmosphere of a halogen corrosive gas and also excellent mechanical property, and a method of producing it.
2. Description of the Related Art
Generally, a process of manufacturing a semiconductor device uses an etching apparatus or sputtering apparatus for subjecting a semiconductor wafer to micromachining, or a CVD apparatus for depositing a film on the semiconductor wafer. These apparatus are provided with a plasma generating mechanism for the purpose of high integration. For example, a helicon wave plasma etching device whose schematic is shown in FIG. 2 is known.
In FIG. 2, reference numeral 1 denotes a processing chamber which is provided with an antenna 2, an electromagnet 3 and a permanent magnet 4 on the periphery. The processing chamber 1 includes an etching gas supplying inlet 5 and a vacuum discharge outlet 6, and also a lower electrode 8 for supporting a semiconductor wafer, which is installed within the chamber. The antenna 2 is connected to a first high frequency power source 10 through a first matching network 9 and connected to a second high frequency power source 12 through a matching network.
Etching by the etching apparatus described above will be carried out as follows. First, with the semiconductor wafer 7 placed on the lower electrode 8, after the interior of the processing chamber 1 has been evacuated, an etching gas is supplied. Next, the antenna 2 and lower electrode 8 are supplied with high-frequency currents at a frequency of 13.56 MHz from the high frequency power sources 10 and 12 through the corresponding matching networks 9 and 11. On the other hand, the electromagnet 3 is also supplied with a current so that a high density plasma is generated within the processing chamber. The plasma energy thus formed decomposes the above etching gas in an atomic state. Thus, the film formed on the upper surface of the semiconductor wafer is etched.
Meanwhile, these apparatus uses as an etching gas a corrosive gas such as a chloric gas inclusive of boron chloride (BCl3) or carbon fluoride (CF4). Therefore, the members exposed to plasma in the atmosphere of the corrosive gas, such as an inner wall of the processing chamber 1, a monitoring window, a microwave introducing window and a lower electrode 8 are required to have a plasma-resistant property. In order to satisfy the above requirement, a ceramics material such as a sintered body of alumina, of sodium nitride, of aluminum nitride, etc. has been used as the plasma resistant material.
However, the ceramics material such as the sintered body of alumina, of sodium nitride, of aluminum nitride, etc. gradually corrodes when it is exposed to the plasma in the atmosphere of the corrosive gas. As a result, the crystal particles constituting the surface are separated so that xe2x80x9cparticle pollutionxe2x80x9d is produced. Specifically, the separated particles deposited on the semiconductor wafer 7 and the lower electrode 8 adversely affect the quality and accuracy of the deposited film. This presents a problem of deteriorating the performance and reliability of the semiconductor device.
In the CVD apparatus also, since the above ceramics material is exposed to a fluorine gas such as fluorine nitride (NF3) under the plasma during the cleaning, it is required to have corrosion resistance.
In order to obviate the problem of corrosion resistance, a ceramics material containing a sintered body of yttrium-aluminum-garnet (YAG) as a raw material has been proposed (JP-A-10-236871). Namely, the proposed ceramics material is a material in which the surface exposed to the plasma in the atmosphere of a halogenic corrosive gas is formed of the sintered body of YAG and has a center line average height (Ra) of 1 xcexcm or less.
However, the sintered body of YAG is excellent in the plasma resistance, but inferior in the mechanical property such as bending strength and breakage toughness. The inferior mechanical property (e.g. fragileness) means that the material is apt to be damaged or broken during a process of cleaning. Being coupled with relative high cost of the material itself, this leads to an increase in the production cost of the manufacturing apparatus or semiconductor.
This invention has been accomplished under the above circumstance, and intends to provide a low-cost ceramics material which has high plasma resistance and is also excellent in the mechanical property such as bending strength and breakage toughness, and a method of producing it.
The first aspect of this invention is a ceramics material characterized by comprising a base material substantially made of a sintered body of alumina and a yttrium-aluminum-garnet(YAG) layer having a thickness of 2 xcexcm or more which is formed on a surface of the base material.
A ceramics material according to the second aspect of this invention, is characterized in that the surface of the base material is covered with the YAG layer so that alumina crystalline particles in the sintered body of alumina are not exposed.
A ceramics material according to the third aspect of this invention is characterized in that the YAG layer has a thickness of 150 xcexcm or less.
A ceramics material according to the fourth aspect of this invention is characterized in that the base material is a sintered body of alumina with an amount of YAG which increases gradually from the interior to the surface.
A ceramics material according to the fifth aspect of this invention is characterized in that an amount of YAG within the sintered body of alumina is 5 weight % or less.
A ceramics material according to the sixth aspect of this invention is characterized in that the alumina crystalline particles in the sintered body of alumina have an average crystalline diameter of 200 xcexcm.
The seventh aspect of this invention is a method of producing a ceramics material comprising the steps of:
preparing a raw powder in which alumina particles having an average particle diameter of 0.1-1.0 xcexcm are mixed with at least a magnesium compound of 0.01-1 weight % in magnesia and an yttrium compound of 0.1-15 weight % in yttria;
molding the raw powder and calcining a molding thus formed; and
heating the molding in an atmosphere containing a hydrogen gas to form YAG which is exuded to the surface to deposit YAG on the surface and sintering the molding.
The eighth aspect of this invention is characterized in that a solution of yttrium is added as a component of the raw powder after the molding has been calcined.
The ninth aspect of this invention is characterized in that a layer of YAG exuded to and deposited on the surface of the sintered molding is heated so that it is densified.
The tenth aspect of this invention producingis characterized in that a layer of YAG exuded to and deposited on the surface of the sintered molding is heated so that it is molten, and solidified again.
The eleventh aspect of this invention is a method of producing a ceramics material, characterized in that a powder layer, molding or a calcined body of YAG is laminated on a molding or a calcined body of alumina containing magnesium and yttrium and is heated in an atmosphere of a hydrogen gas.
The twelfth aspect of this invention is a method of producing a ceramics material, characterized in that a powder layer, molding or a calcined body of YAG is laminated on the surface of a sintered body with a YAG layer deposited thereon and is heated in an atmosphere of a hydrogen gas so that it is sintered.
In these aspects of this invention, it seems that the surface of the base material of alumina substantially made of a sintered body of alumina is covered with the YAG layer through its exuding for the following matters. The yttrium component which resides on the surface of the alumina raw particle is deformed into YAG through heating, and the boundary among the alumina particles is decreased owing to the growth of the alumina particle. As a result, the YAG cannot reside at the center of the sintered body of alumina so that the major amount of it gradually move to the surface of the sintered body.
In this inventions, the YAG layer covering the surface of the base material of alumina is required to have a thickness of 2 xcexcm or more. Specifically, where the thickness is shorter than 2 xcexcm required plasma resistance cannot be given. Further, the surface of the base material of alumina is preferably covered with the YAG layer so that the base material of alumina is not exposed to the surface. Where the base material of alumina is exposed, when the YAG layer is exposed to plasma in an atmosphere of a corrosive gas, the exposed portion of the base material will partially corrode so that fine particles are apt to occur. Furthermore, the thickness of the YAG layer is preferably not greater than 150 xcexcm. The thickness exceeding 150 xcexcm does not provide an improvement of the effect, but is a hindrance of low production cost.
The base material substantially made of a sintered body of alumina means that the main component of the base material is the sintered body of alumina. Particularly, it is preferably the sintered body in which the composition of alumina is 85 weight % or more. Further, where the YAG layer is formed as a coating through breaching when the alumina is sintered, the ceramics material can exhibit plasma resistance and a mechanical property.
In the structure in which the surface of the base material of alumina is covered with the YAG layer, where the base material of alumina is a sintered body of alumina with an amount of YAG which increases gradually from the interior to the surface, a difference in the thermal expansion coefficient between the base material of alumina and YAG layer is reduced. Therefore, a ceramics material with improved separation resistance during the heating cycle is provided.
The amount of YAG in the interior of the sintered body of alumina is preferably 5 weight % or less in order to provide the ceramics material with higher breakage toughness, more preferably 3 weight % or less. In the case of the ceramics material of which the entire outer surface is covered with the YAG layer, the interior of the base material of alumina refers to the vicinity of center of gravity. Incidentally, the member which is obtained by optionally cutting the ceramics material with the entire outer surface covered with the YAG layer in order to give plasma resistance to a specific plane of the base material should be also included in the category of the ceramics material herein referred to.
The average particle diameter of the sintered crystal in the base material of alumina (sintered body of alumina) is preferably 200 xcexcm or less, more preferably 5-200 xcexcm, and much preferably 10-40xcexcm. If the average particle diameter exceeds 200 xcexcm, it is difficult to disperse uniformly gradually the amount of YAG which increases gradually from the interior of the sintered body of alumina to the surface. Namely, YAG is apt to reside locally. This make it difficult to provide higher separation resistance during the heating cycle of the YAG layer. The particle diameter is a value measured by the planimetric technique.
In the sintering step of the ceramics material, where the YAG layer is formed through exuding on the surface of the base material of alumina, magnesia (which can be replaced by the hydrate of magnesium sulfate and magnesium nitrate) of 0.01-1 weight % is preferably added to control the growth of crystalline particles.
The ceramics material in this invention can be produced by the method defined in this invention. Generally, a raw powder is prepared in which alumina particles having an average particle diameter of 0.1-1.0 xcexcm are mixed with at least a magnesium compound of 0.01-1 weight % in magnesia and an yttrium compound of 0.1-15 weight % in yttria.
After the raw powder has been granulated, it is molded by e.g. hydrostatic pressure press, and the molding thus formed is subjected to calcination processing. The molding thus obtained is heated in an atmosphere containing a hydrogen gas to form YAG which is exuded to the surface through the grain growth of alumina to make a YAG film. The molding is further sintered to provide a desired ceramics easily.
Incidentally, the granulated raw power may be molded by not the hydrostatic pressure press but may be molded by other molding means such as extrusion, injection molding, casting, etc. Further, when the raw powder may be prepared, in place of making particles as the solution containing yttrium, yttrium or its compound particles (powder) is added/mixed as long as it can be uniformly scattered.
The average particle diameter of the alumina particle which is the main component of the raw powder is preferably selected in a range of 0.1-1.0 xcexcm. This is because the crystalline particle of alumina makes abnormal growth during a final sintering step, which may ruin the exuding of YAG to the surface and its deposition.
The addition of magnesia is done in order to control appropriately the crystalline particles of the sintered body which is the base material having the alumina as a main component. The composition ratio is selected in a range of 0.01-1 weight %. Incidentally, the composition of magnesia to be added/mixed may be a magnesium compound which is deformed into magnesia by heating such as magnesium sulfate, magnesium nitrate, etc. In this case, its adding/mixing amount should be selected in a range of 0.01-1 weight %.
The addition of the solution containing yttrium is efficient to generate required YAG which is exuded to and deposited on the surface of the sintered body of alumina and improve plasma-resistance. It is selected to be 0.1-15 weight % in yttria. It should be noted that the solution containing yttrium is obtained by dissolving one or two or more of yttrium acetate, yttrium chloride, or their hydrate in pure water, alcohol, etc.
In this invention, the raw powder containing the alumina particles as a main component is mixed/stirred with magnesia, yttrium composition, binder resin and medium solution to prepare a slurry. This is carried out using e.g. a rotary ball milling. The slurry thus prepared is granulated using e.g. a spray drier. The granulated powder is molded by an ordinary pressuring molding such as hydrostatic press, extrusion, injection molding, or casting.
The molding of the granulated powder is calcined at a temperature of 600-1300xc2x0 C. under an atmospheric pressure. The temperature and time of the calcination is determined according to the shape and size of the molding. The sintering after the calcination is carried out at a temperature of 1700-1850xc2x0 C. in an atmosphere containing a hydrogen gas such as a hydrogen current.
In this case, in order to form YAG more smoothly and advance its exuding to and deposition on the surface while suppressing the abrupt growth of crystal particles, the temperature rising speed is selected and set at a slightly slow speed, or the sintering time is set at a longer time.
In this invention, the YAG formed during the calcination and sintering step and exuded and deposited on the surface is heated for the purpose of densifying by the YAG layer. Specifically, where the YAG film exuded to and deposited on the surface of the sintered body is thin or coarse, it is heated at the temperature of e.g. 1700xc2x0 C.-1850xc2x0 C. Thus, the YAG exuded to and deposited on the surface is softened and dissolved again, thereby improving plasma-resistance.
The ceramics material can be produced in the following process. In this invention, a molding or a calcined body of alumina containing magnesium and yttrium is prepared, and a powder layer, molding or a calcined body of YAG is laminated on the surface of the molding or calcined body thus prepared. The laminated body is heated in an atmosphere of a hydrogen gas so that it is sintered. Otherwise, a powder layer, molding or a calcined body of YAG is laminated on the surface of the sintered body with a YAG layer deposited thereon. The laminated body is heated in an atmosphere of a hydrogen gas so that it is sintered.
In this inventions, a structure is adopted in which a base material is substantially made of an sintered body of alumina and the surface thereof is covered with a YAG layer. Specifically, the structure is adopted in which the base material is made of an sintered body of alumina with an excellent mechanical property such as bending strength and breakage toughness while the surface exposed to plasma is covered with the YAG layer with excellent plasma-resistance.
Where the base material is an sintered body of alumina with an amount of YAG which increases gradually from the interior to the surface, it exhibits high heat-resistance. The coverage of the YAG layer improves the plasma resistance of the ceramics material, and cancels the occurrence of damage/breakage during the cleaning. Thus, the ceramics material which is free from the fear of particle contamination and has excellent heating-cycle resistance can be acquired.
Therefore, this invention suppresses the increase in the production cost of a producing apparatus and semiconductor and also efficiently contributes to the production/processing of the semiconductor with high performance and reliability without adversely affecting the quality and accuracy of the deposited film.
This invention can provide, with high yield and in mass production, a ceramics material in which the base material is made of a sintered body of alumina with an excellent mechanical property such as bending strength and breakage toughness while the surface exposed to plasma is covered with the YAG layer with excellent plasma-resistance. Particularly, this invention can easily adopt the structure in which the YAG is exuded to and deposited on the surface of the base material of the sintered body of alumina with an amount of YAG which increases gradually from the interior to the surface, and so can provide a ceramics material with excellent thermal shock resistance.